1. Field of the Invention
The present invention relates to an elastic sealing member for a resin fuel tank for a vehicle.
2. Description of the Related Art
In a fuel tank for a vehicle, a pump unit is mounted. The pump unit has a base body in which parts and components such as a fuel pump are assembled, a fuel in the fuel tank is pumped up by the fuel pump and delivered to an engine side via an outlet piping.
In a conventional structure for mounting the pump unit to the fuel tank, the fuel tank is provided with a cylindrical wall portion upright from an outer surface of a tank body of the fuel tank. And, the pump unit is inserted into the fuel tank through an opening portion on an upper end of the cylindrical wall portion of the fuel tank such that a flange portion of the base body of the pump unit is placed on an upper end surface of the cylindrical wall portion. In this state, a screw-on cap is screwed on an externally threaded portion formed on an outer peripheral surface of the cylindrical wall portion to sandwich the flange portion of the base body by the upper end surface of the cylindrical wall portion and the screw-on cap, in an axial direction of the cylindrical wall portion, namely in a vertically direction. Thereby the pump unit is mounted to the fuel tank.
When the pump unit is mounted to the fuel tank, an air-tight seal is required between the cylindrical wall portion of the fuel tank and the pump unit, specifically the base body of the pump unit. For this purpose, an elastic sealing member is interposed between the cylindrical wall portion and the base body of the pump unit.
Conventionally, a fuel tank made of metal has been used, and a plate-like elastic sealing member 200 shaped of a ring as shown in FIG. 7 has been used as such a elastic sealing member. The elastic sealing member 200 includes upper and lower flat surfaces.
Specifically, such plate-like elastic sealing member 200 is interposed between the flange portion of the base body and the upper end surface of the cylindrical wall portion, and a screw-on cap is tightened. Under its tightening force, the elastic sealing member 200 is pressed in an axial direction by the flange portion of the base body and the upper end surface of the cylindrical wall portion, and is compressed and elastically deformed. In this manner, an air-tight seal is provided between the base body and the cylindrical wall portion.
In this case, since the metal fuel tank has high-mechanical strength, when the screw-on cap or nut is tightened with large screw torque, the fuel tank itself is not deformed, and the elastic sealing member 200 is sufficiently compressed and elastically deformed to exhibit a good sealing function.
On the contrary, recently, in view of weight saving of a tank, a resin fuel tank has been increasingly used for such a fuel tank. If above such sealing structure is adapted for this case (the resin fuel tank), when the above screw-on cap is firmly tightened, a cylindrical wall portion made of resin is deformed due to load produced by tightening the screw-on cap, and there is a fear that a stable sealing performance cannot be achieved. In order to solve this problem, an elastic sealing member 202 shown as an example in FIGS. 8 and 9 is proposed as an elastic sealing member for the resin fuel tank.
The elastic sealing member 202 shown in the FIGS. 8 and 9 is the one disclosed in Patent Document 1 below. The elastic sealing member 202 has a cylindrical sealing portion 204 and a flange sealing portion 206 of annular shape, projecting radially outwardly on an upper end of the cylindrical sealing portion 204.
Meanwhile, in FIG. 8, reference numeral 208 indicates a resin fuel tank, and reference numeral 210 indicates a tank body. The resin fuel tank 208 is provided integrally with a cylindrical wall portion 212 of cylindrical shape, upright from an outer surface (an upper surface in the figure) of the tank body 210.
The cylindrical wall portion 212 has an opening portion 214 on an upper end thereof, and further, an externally threaded portion 215 in an outer peripheral surface thereof.
Reference numeral 216 indicates a pump unit that is constructed by assembling components such as a fuel pump (not shown) in a base body 218 in unitary relation. The pump unit 216 is formed with a flange portion 220 of annular shape, projecting radially outwardly on an upper end of the base body 218, and further with a fit portion 222 fitting to an inner peripheral surface of the cylindrical wall portion 212 via the elastic sealing member 202, under the flange portion 220 in the figure.
Reference numeral 224 indicates a screw-on cap that has an internally threaded portion 226 in an inner peripheral surface thereof, and a radially inwardly directed annular flange portion 228, on an upper end thereof in the figure.
As shown enlarged in FIG. 9, the radially outwardly directed flange sealing portion 206 of the above elastic sealing member 202 is formed with main sealing protrusions 230, 231 of semicircular cross-section, protruding from flange surfaces of front (outer) and back (inner) sides. Each of the main sealing protrusions 230, 231 extends annularly in a circumferential direction and along the flange sealing portion 206.
And, an outer peripheral surface of the cylindrical sealing portion 204 is formed with sub sealing projection 232 projecting radially outwardly. The sub sealing projection 232 extends annularly in a circumferential direction along the outer peripheral surface of the cylindrical sealing portion 204.
Here, the sub sealing projection 232 is entirely angled, downwardly in the figure, namely, in an inserting direction of the pump unit 216 in the cylindrical wall portion 212.
And, the sub sealing projection 232 has a triangle cross-sectional shape including a sharp point, and the triangle cross-sectional shape has a wall thickness in a vertical direction (axial direction) in the figure that gradually decreases from its base toward its leading end.
The elastic sealing member 202 performs a sealing function as follows.
With reference to FIG. 8, for mounting the pump unit 216 in the fuel tank 208, first, the elastic sealing member 202 is attached in the cylindrical wall portion 212 of the fuel tank 208 with the screw-on cap 224 removed, and the pump unit 216 is inserted inside the fuel tank 208 through the opening portion 214 of the cylindrical wall portion 212.
And then, the screw-on cap 224 is turned on the cylindrical wall portion 212 and screwed on the externally threaded portion 215 of the cylindrical wall portion 212 until screwing torque or a deformation volume is achieved as predetermined.
When the screw-on cap 224 is completely screwed thereon, the flange sealing portion 206 is sandwiched by the flange portion 220 of the base body 218 of the pump unit 216 and an outer end surface 212A of the cylindrical wall portion 212, in a vertical direction in the figure. At that time, mainly the main sealing protrusions 230, 231 formed on the flange sealing portion 206 are compressed and elastically deformed, in a vertical direction in the figure, and thereby provides an air-tight seal between the flange portion 220 of the base body 218 and the upper end surface 212A of the cylindrical wall portion 212 along their entire circumferences.
The reason why the above elastic sealing member 202 for the resin fuel tank 208 is provided with the above cylindrical sealing portion 204 and the above sub sealing projection 232 is as follows.
The resin fuel tank 208 has less mechanical strength compared to a fuel tank made of metal, and there is a fear that when the screw-on cap 224 is firmly tightened, the cylindrical wall portion 212 is deformed.
When the cylindrical wall portion 212 is deformed, there is a fear that a sealing performance of the flange sealing portion 206 becomes insufficient.
So, the elastic sealing member 202 for the resin fuel tank 208 is provided with the cylindrical sealing portion 204, and the sub sealing projection 232 is formed so as to project from its outer peripheral surface, and further, the sub sealing projection 232 is designed to elastically contact an inner peripheral surface of the cylindrical wall portion 212 of the fuel tank 208 and thereby provide a seal supplementarily. Namely, the sub sealing projection 232 functions as a secondary seal.
And, since the resin fuel tank 208 is formed typically by blow molding, a wall-thickness of the cylindrical wall portion 212 tends to be nonuniform in a circumferential direction, and accordingly, a shape of the inner peripheral surface of the cylindrical wall portion 212 tends to be uneven along the circumferential direction.
In addition, when the cylindrical wall portion 212 is deformed by tightening the screw-on cap 224, in some cases, the inner peripheral surface of the cylindrical wall portion 212 defines a irregular shape instead of a perfect circular shape. In order to ensure a secondary seal by the sub sealing projection 232 even in this case, a projecting length or height of the sub sealing projection 232 with respect to the cylindrical sealing portion 204 is increased such that an outer diameter defined by a leading end of the sub sealing projection 232 is larger than an inner diameter of the cylindrical wall portion 212 by certain length, and thereby the sub sealing projection 232 is ensured to elastically contact the inner peripheral surface of the cylindrical wall portion 212.
And, in order that the leading end portion of the sub sealing projection 232 is surely deformed so as to follow a shape of the inner peripheral surface of the cylindrical wall portion 212, the sub sealing projection 232 has a wall thickness thin at its leading end portion and has a triangle cross-sectional shape including an acutely sharp point.
However, it is found that the sub sealing projection 232 having the triangle cross sectional shape including such acutely sharp point causes a following problem.
That is, when deformation or deformation state of the sub sealing projection 232 is observed precisely, as shown in FIG. 10, a fact is found that an outer peripheral end portion of the sub sealing projection 232, namely the leading end portion thereof is deformed in an undulate manner or wave manner.
When the leading end portion of the sub sealing projection 232 is deformed in such wave manner, a clearance is created with respect to the inner peripheral surface of the cylindrical wall portion 212 and there is a fear that a sufficient seal performance cannot be ensured.
Meanwhile, an elastic sealing member for a resin fuel tank similar to the above is also disclosed in Patent Document 2 below.
[Patent Document 1]JP-A, 2004-293459[Patent Document 2]JP-A, 2004-278622
Under the circumstances described above, it is an object of the present invention to provide an elastic sealing member for a resin fuel tank that can ensure a secondary seal or backup performance (or backup seal performance) by a sub sealing projection in case that a cylindrical wall portion of a resin fuel tank where the elastic sealing member is attached has an inner peripheral surface that is not necessarily shaped of a perfect circle or has a shape varied in a circumferential direction.
And, it is another object of the invention to provide the elastic sealing member that can favorably prevent deformation of the cylindrical wall portion created by tightening of a screw-on cap or nut, and can perform a good sealing function by a sub sealing projection, and further by a main sealing protrusion.